Overview of shortness of breath Flashcards
(30 cards)
What is the partial pressure of oxygen in dry air?
Around 21.2 kPa at sea level
Wwhat is hypoxaemia
abnormally low arterial partial pressure of oxygen (Pa02)
What is hypoxia?
Hypoxia is defined as a low tissue partial pressure of oxygen either due to a reduction the supply of oxygen or the ability to use it.
WWhat is the classic sign of hypoxaemia?
central cyanosis
What is Aa difference
Aa difference = PA02 — PaO2
How do you find PAO2
Calculated using alveolar gas equation
How do you find PaO2
Measured by performing an arterial blood gas analysis
What is Aa difference in young adults?
2kPa
What is Aa difference in elderly?
5kPa
What are the causes of hypoxaemia Give examples for each effect
High altitude e.g. climbing Everest Hypoventilation e.g opioid overdose Diffusion defect e.g fibrosis VA:Q mismatch e.g pulmonary embolism Right-to-to left cardiac shunt e.g congenital cyanotic heart disease
How does High altitude affect Aa difference
Normal
How does Hypoventilation affect Aa difference
Normal
How does Diffusion defect affect Aa difference
Increased
How does VA:Q mismatch affect Aa difference
Increased
How does Right-to-to left cardiac shunt affect Aa difference
Increased
What are the causes of tissue hypoxia
Hypoxaemia
Stagnant hypoxia
Anaemia hypoxia
Histotoxic hypoxia
When should you suspect hypoxia?
Anxiety Euphoria Confusion/poor judgemental/irritability Lack of coordination Tachypnoea, use of accessory muscles Poor coordination Tunnel-vision Loss of consciousness/coma Seizures
Clinical features of type II respiratory failure
Vary according to the underlying cause
Headache (cerebral vasodilatation)
Flapping tremor of wrist
Bounding pulse
What is the MRC Dyspnoea
Grade:
1 Not troubled by breathlessness except on strenuous exercise
2 Short of breath on hurrying or walking up a slight hill
3 Walks slower than contemporaries on level ground, or has to stop for breath when walking at own
pace
4 Stopes for breath after about 100m or after a few minutes on level ground
5 Too breathless to leave the house, or breathless when dressing or undressing
Why does high altitude cause hypoxaemia
Fall in barometric pressure
leads to a decrease in PLO2
and PAO,
Why does hyperventilation cause hypoxaemia
Decreased alveolar ventilation ‘pump failure’
Leads to a decrease in PAO2
Increase Increase PACO2
Why does diffusion defect cause hypoxaemia
Leads to a decrease in Pa02
Why does VA:Q mismatch cause hypoxaemia
Leads to a decrease in PaO2
PACO2 low or normal
Why does right to left cardiac shunt cause hypoxaemia
Shunted blood bypasses the alveoli and cannot be oxygenated resulting in a very low Pa02
